1. The Field of the Invention
The present invention relates generally to controlling the delivery of ink to one or more print heads and, more specifically, generally relates to controlling the pressure of ink delivered to one or more print heads from an ink reservoir.
2. The Relevant Technology
Printing devices, such as ink-jet printing devices, are well known and available from various manufacturers. A typical ink-jet printing device includes multiple print heads mounted on a movable carriage. Each print head contains one or more ink-jet nozzles through which ink is delivered during a printing process. For instance, as the movable carriage is repeatedly scanned back and forth across a printable medium, such as a paper sheet, the ink-jet nozzles in the various print heads are activated to lay or deliver drops of ink on the printable medium at precise locations. In typical color printing, between four and six different colors of ink are deposited over an area by multiple heads, in successive scans across the sheet.
Following a print pass, relative movement between the printing device and the medium is provided. This relative movement enables a different portion of the medium to be printed during each subsequent scan. As those skilled in the art will appreciate, the nozzles on each of the multiple print heads must be controlled to deposit ink drops in precise locations relative to drops deposited by the other print heads. The control of the ink delivered from the nozzles has a profound effect upon the quality of images created by ink jet printers.
To maintain high quality while depositing ink at fast rates, it is important that all deposited ink drops have substantially the same volume so that all printed drops are consistent in size. When the volume of deposited ink is either excessive or insufficient, differences in the printed image are perceptible. These differences in the printed image quality may occur when a meniscus of the ink at one or more nozzles extends beyond the boundaries of the specific nozzle to encroach upon one or more of the surrounding nozzles. The encroaching of the ink results in excessive ink deposited upon printable media during a print process, thereby reducing the image quality. Further, the excessive ink can solidify over one or more of the nozzles and prevent ink from being deposited upon printable media during a printing process. Again, this reduces the image quality of the printed image.
Additionally, differences in printed image quality can occur when the meniscus of ink at a nozzle becomes concave and extends inwardly through the nozzle and into the print head. When this occurs, insufficient ink is deposited from the print head, resulting in decreased image quality. Furthermore, when a curvature of the meniscus exceeds specific limits governed by the surface tension characteristics of the ink and the adhesion of the ink to the nozzle, the meniscus can break. When the meniscus breaks, ink xe2x80x9cdroolsxe2x80x9d from the nozzle before, after and during a printing process. This again results in reduced image quality of the printed image.
Many attempts have been made to control the volume of ink deposited from the print nozzles. Further, many attempts have been made to control the curvature of the meniscus of the ink at the nozzles to prevent insufficient or excessive amounts of ink from being deposited upon printable media during a printing process.
In numerous ink-jet printers, ink is delivered to each print head by a tube that connects the print head to an ink reservoir positioned above the vertical level of the print head. During the printing process, ink flows along the tube to the nozzle of the print head under the force of gravity as the weight of the ink within the ink reservoir forces the ink stored in the tubing toward the nozzles. The volume of ink forced to each nozzle depends upon the particular volume of ink stored in the ink reservoir, fluid dynamic characteristics of the tubing, and chemical characteristics or properties of the ink. For instance, when an ink having a high absolute viscosity is employed with a printing device, a low volume of ink is forced to a nozzle under a given pressure. Similarly, when an ink having a low absolute viscosity is employed with a printing device a high volume of ink is forced to a nozzle under the same given pressure. Changes to the chemical composition of the ink causes changes in the effectiveness of these gravity-type ink-jet printers. Therefore, these ink-jet printers are difficult to use with a variety of different inks.
Other ink jet printers utilize a surge suppressor to pressurize the ink as it is passed into the ink reservoir. The surge suppressor maintains an average pressure within the tube connecting the ink reservoir with the print head. Typically, the surge suppressor used in such ink-jet printers is designed for a particular ink, with associated characteristics and properties. Additionally, surge suppressors are typically not adjustable and allow large ranges of pressure fluctuations.
Consequently, it would be an advance in the art to provide systems and methods that maintain high quality image reproduction through control of the volume of ink deposited from a nozzle of a print head. Further, it would be an advance in the art to provide systems and methods that control the curvature of the meniscus, while preventing insufficient or excessive deposit of ink during a printing process.
In accordance with the invention as embodied and broadly described herein, a printing system capable of delivering ink to printable media is disclosed. One particular printing system includes a printing device that communicates with a vacuum pump and a remote main ink reservoir. During a printing process, the remote main ink reservoir delivers ink to the printing device to maintain the ink stored in an ink reservoir of the printing device within selected tolerances. Meanwhile, the vacuum pump creates a vacuum or partial vacuum within the ink reservoir to maintain a pressure of the ink within selected tolerances so that the ink is delivered from a print head during the printing process. Through operation of the vacuum pump, the pressure exerted by the ink at one or more nozzles of the print head is maintained with desired tolerances no matter the particular volume of ink stored within the ink reservoir. Consequently, the potential for excessive or insufficient delivery of ink from the print head is reduced or eliminated.
According to one aspect of one embodiment of the present invention, a provided printing device includes a housing with a printer head carriage mounted to and slidable upon a track. The printer head carriage supports one or more ink reservoirs that communicate with a vacuum pump and a remote main ink reservoir. Disposed within one or more of the ink reservoirs are sensors to identify a level of ink and a vacuum or partial vacuum level within the one or more ink reservoir. These sensors send signals indicative of the sensed levels to a controller that is adapted to control the operation of the vacuum pump and an ink pump associated with the remote main ink reservoir to maintain the level of ink and the vacuum or partial vacuum level within desired tolerances.
According to another aspect of one embodiment of the present invention, a printing device communicates with an accumulator, which is disposed between the printing device and the vacuum pump. The accumulator functions to increase the resolution, the accuracy, and the precision of the vacuum pump. In this manner, the printing system can accurately control the vacuum or partial vacuum level within the ink reservoir and hence maintain the pressure of the ink at the one or more nozzles of the one or more print heads.
According to another aspect of one embodiment of the present invention, a printing system includes a vacuum pump that communicates with an ink reservoir of the printing device. The vacuum pump can degas the ink stored within or communicating with the ink reservoir to allow gas dissolved within the ink to migrate to and escape from a surface of the ink. This can be achieved, in one configuration, by creating a vacuum or partial vacuum within the ink reservoir.
According to another aspect of one embodiment of the present invention, a printing system is adapted to accommodate the use of multiple types of ink. The printing system includes a vacuum pump that is used to control the level of a vacuum or partial vacuum within an ink reservoir. A controller changes a level of vacuum or partial vacuum based upon the level of ink within the ink reservoir to achieve a desired pressure at one or more nozzles of one or more print heads. The inks used within the printing system can each have different chemical compositions and hence different flow characteristics that govern the manner in which the ink flows from the ink reservoir, along one or more tubes, to the one or more print heads. When ink reservoirs with a second type of ink are substituted for ink reservoirs with a first type of ink, the controller can vary the level of vacuum or partial vacuum to accommodate for changes in ink characteristics between the first and second types of ink, such as but not limited to, changes in adhesions, surface tension, viscosity, or other characteristics of the inks.
According to another aspect of one embodiment of the present invention, by creating a vacuum or partial vacuum within an ink reservoir, a printing system can control the size, shape, and configuration of a meniscus of the ink formed at one or more nozzles of one or more print heads. In addition to the degree of attraction of the ink to the material forming the nozzles and the surface tension characteristics of the ink, the curvature of the meniscus is affected by the pressure exerted by the column of ink extending from the nozzle to the exposed surface of the ink within the ink reservoir. Through varying the level of the vacuum or partial vacuum within the ink reservoir, embodiments of the printing system can change the curvature of the meniscus to control the volume of ink to be delivered from the nozzles and limit the meniscus from rupturing or extending onto the outer surface of the print head.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.